Chemical kinetic modeling development and validation experiments for direct fired sCO2 combustor PI: Dr. Subith Vasu Center for Advanced Turbomachinery and Energy Research (CATER) Mechanical and Aerospace Engineering Department University of Central Florida, Orlando, FL 32816 DE-FE0025260 Duration 3 years: 10/1/2015-9/30/2018 UTSR Project kickoff meeting 1
Project Summary Develop a chemical kinetic mechanism for Supercritical Carbon Dioxide (sCO 2 ) Mixtures Validate the chemical Kinetic Mechanism with shock tube experiments Develop a CFD Code that utilizes mechanism for sCO 2 combustors 2
Motivation Current state-of-the-art, such as GRI-3.0 Mechanism, has only been validated for pressures up to 10 atm Mechanisms have not been developed for CO 2 diluted mixtures Updated mechanism will allow for accurate combustor modeling with multi-step combustion using a validated mechanism Current CFD combustion models do not consider non-ideal effects 3
Roles of Participants Subith Vasu, PI: Administrative Tasks, Shock Tube Experiments and Development of Chemical Kinetic Mechanism Co-PI’s Artem Masunov: Reaction Rate Calculations and Development of Chemical Kinetic Mechanism Ron Hanson, David Davidson: Shock Tube Experiments Scott Martin: CFD Combustion Model Jayanta Kapat, David Amos: sCO2 Cycle, Project Management and Technical Advising 4
List of Tasks 1.1 Project Management and Revisions 3.4 High Pressure species time-histories 1.2 Project Reporting 4.0 Detailed Chemical Kinetic Mechanism 2.0 Kinetics Data at Low/Medium for CH4 combustion Pressures 4.1 Adopt a Mechanism for Methane 2.1 Ignition Delay Times at Low/Medium Combustion and Determine Key Pressures in CH4/O2 Reactions 2.2 Ignition Delay Measurements at 4.2 Update Key Reaction List Using Real Low/Medium Pressures for Gas Equation of State Syngas/O2 4.3 Boxed Molecular Dynamics 2.3 Low/Medium Pressure Species Time- Simulations histories 4.4 Mechanism Validation 3.0 Kinetics Data at High Pressures 5.0 sCO2 CFD Development 3.1 High Pressure Equation of State 5.1 Modify OpenFOAM CFD code for real 3.2 Ignition Delay Times at High gases, validate with available data Pressures up to 300 bar for CH 4 /O 2 5.2 Implement CMC combustion model to 3.3 Ignition Delay Times at High allow very large mechanisms Pressures up to 300 bar for 5.3 Perform design studies of concept Syngas/O 2 burners with CFD 5
Shock Tube Experimentation Experiments will be performed in two different shock tube facilities for Methane Oxidation diluted with CO 2 and Argon Experiments will be performed pressures up to 300 Bar for temperatures between 800 K and 2000 K and equivalence ratios of 0.7 to 1.2 Ignition delay times and key species time histories will be measured Experiments will also be performed for selected mixtures of syngas 6
Combustion chemistry Fuel + O 2 EXPERIMENT MODEL Reaction Kinetic Initial H-Abstraction Mechanism Targets Decomposition & Oxidation Development (Shock Tubes) Products Products 1. Decomposition 1. Ignition Time Pathways Measurements Intermediate Species 2. Intermediate 2. Species Species Sub-Mechanisms OH, CH 3 , C 2 H 4 , C 2 H 2 , H 2 , CO, etc. Time-Histories 3. Full Mechanisms 3. Direct Rate Ignition Measurements 4. Reduced Mechanisms 5. Validation CO, CO 2 , H 2 O 7
Shock tube operation: Pre-shock filling Pressure Optical transducers Diaphragm diagnostics for absorption, 4 1 emission High P Low P Driver section Driven section (high-pressure) (low-pressure) Shock tubes are ideal for studying combustion chemistry Step change in T, P and well-defined time zero Simple fuel loading Accurate mixtures and pre-shock conditions 8
Shock tube x-t diagram 0 5 10 15 20 25 Spatially Uniform High Temperature and Pressure Test Region * Test Time (~2-40ms) Driver Expansion Reflected Fan Time [ms] Shock Contact Driven Section Driver Surface Incident -2 0 2 4 6 8 Diaphragm Shock Front Position (x) [m] Particle Path 9
UCF shock tube facility Graduate students Joseph Lopez, Owen Pryor, Batikan Koroglu, and Prof. Vasu in their lab Advantages of shock tubes Near-ideal constant volume reactor Well-determined initial T and P Optical access for laser diagnostics UCF shock tube facility Large diameter shock tubes (14 cm) Heatable to 150 ° C Aerosol capability T=600-3000 K, P=0.1-50 atm Tailored gases, extended drivers up to 50’ provide long test times (~ 40 ms) Optically accessible end sections for diagnostics and imaging studies 10
Ignition Delay Time Measurements for Low Pressures Ignition delay times measured from the arrival of reflected shockwave to rise of the pressure trace Arrival of shockwave determined as midpoint of the second pressure rise (rise due to reflected shock) Rise of OH Emissions measured as the intersection between the baseline and the tangent line drawn from maximum rise of OH 11
Concentrations of Key Species using Laser Absorption Concentrations of key species will be measured up to the time of ignition Species time-histories are measured using a peak-valley measurement scheme to remove interfering species Absorption is measured using the Beer-Lambert law and comparing the intensity of light in the mixture with the intensity under vacuum I I − = α ν = φ = β = σ ν − = α + α + τ ln( ) ( , T , P ) S PL PL ( , T , P ) nL ln( ) ν ν ν ν interferen ce extinction I I o o 12
Methane Sensor Using 3.4um Quantum-Cascade Laser • Methane concentration measurement set up and detectivity showing less than 10 ppm at 800K. • We have diagnostics for other species (H 2 O, CO, CO 2 ) and Temperature 13
Methane Ignition and Concentration Results from UCF (journal paper in review as of 10/2015) • Comparison of measured and simulated methane concentration for – Stoichiometric ignition of 3.5% CH 4 in argon – GRI predictions are wrong for both ignition time and concentrations even at low pressures !! 0.15 2.5 X CH4 (Measured) CH* P = 0. 70 atm GRI Aramco Pressure X CH4 (Aramco) P = 3.58 atm GRI Aramco Ignition Delay Time [ µ sec] 2.0 X CH4 (GRI) 1000 P [atm] / CH* 0.10 1.5 X CH4 1.0 0.05 100 0.5 30 %CO 2 Φ = 2 0.00 0.0 0.48 0.52 0.56 0.60 0.64 0 500 1000 1500 2000 1000/T [1/K] Time [ µ sec] 14
Existing High-Pressure Ignition Data CH 4 /O 2 /N 2 /Ar ignition delay time measurements. The higher pressure data exhibit a significantly weaker variation with temperature (smaller activation energy) than the lower pressure, higher temperature mixtures JPP, 1999, 15(1), 82-91 15
Chemical Kinetic Mechanism Summary • Combustion Kinetics of C 0 -C 6 hydrocarbons includes 1161 species and 5622 elementary reactions (RD2010) • Existing kinetic models are only valid at low pressures • We will use multiscale modeling approach to extend their validity to above 300 bar by: 1. Quantum Mechanic simulations of the activation enthalpies in gas vs. CO 2 environment 2. Boxed Molecular Dynamic simulations of reaction processes 16
The important elementary steps in RD2010 mechanism of C0-C4 fuel combustion C.V. Naik, K.V. Puduppakkam, E. Meeks, J Eng Gas Turbines Power 2012 , 134, 021504. 17
Quantum Chemical calculations in the framework of Transition State Theory (TST) Experimental rate constant is often analyzed in terms of modified Arrhenius equation: According to transition state theory (TST), the bimolecular reaction A+B→C is approximately considered as a two-step process: A..B ↔TS→ C Here the transition state (TS, a.k.a. activated complex AB ≠ ) is formed in a reversible step and coexists in thermal equilibrium (as governed by Boltzmann statistics) with the reaction complex A..B, and is converting to the product C irreversibly. Quantum Chemical methods are then used to obtain the enthalpy and entropy of the activated complex: Δ H ≠ and Δ S ≠ : The Δ H ≠ is then approximately corresponds to E a from Arrhenius equation; Δ H ≠ is always positive. Zero Δ H ≠ values require free energy potential surface, as described by Variational TST (VTST). Negative values of E a can be observed as a result of decreased equilibrium concentration of A..B at higher temperatures prior to TS formation: A+B ↔ A..B 18
Elementary Reaction O2+H→ O+OH • Five distinct steps along Reaction Coordinate: 1. Reactants (R1,R2) 2. Reactive complex (RC) 3. Transition state (TS) 4. Product complex (PC) 5. Products (P1,P2) • Two radicals may couple high spin or low spin; these result in two reaction surfaces with two different multiplicities • QST3 method will be used to locate Transition state • IRC method will be used to confirm Transition state 19
Synchronous Transit-guided Quasi-Newton method is used to locate TS structure TS • TS is the first order saddle point on Potential Energy Surface, that is a maximum in one direction, and a minimum in all other directions. • In order to find the structures of the transition states we use the Synchronous Transit-guided Quasi-Newton method implemented in Gaussian09 via one of the two keywords: QST2 (coordinates for the reagents and products are needed as input) or QST3 (where coordinates for the TS structure guess is needed also). 20
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